The present invention generally relates to a copper foil with a blackened surface or layer, and in particular relates to a copper foil with a blackened surface or layer that is especially useful for a plasma display panel (PDP) and has superior shielding characteristics of effectively shielding electromagnetic waves, near infrared rays, stray light, outside light and the like.
Recently, a plasma display panel (PDP) characterized in that it is easy to manufacture a large-sized screen and having a fast drive speed is being used in various display devices at a staggering rate.
This plasma display panel has a structure and function of generating plasma with a gaseous discharge, exciting phosphor disposed in the cell with the line spectrum of the generated ultraviolet range, and generating light of a visible region.
When plasma is generated with a gaseous discharge as described above, in addition to the line spectrum of an ultraviolet range used in phosphor, a line spectrum of a wavelength in a wide range up to the near infrared region will be generated.
Since the wavelength of the near infrared region generated from the plasma display panel described above is close to the wavelength used in optical communication, there is a problem in that a malfunction will occur when the two wavelengths are positioned at a close range, and the generation of electromagnetic waves such as microwaves and infrasonic waves will also become a problem.
A shield layer formed from a copper foil is generally provided to the front face of the panel in order to shield the leakage of electromagnetic waves or the line spectrum of the near infrared region. Normally, this copper foil is formed into a thin linear mesh shape by etching and configures a shield layer. Incidentally, resin such as PET is further coated on the top surface of this copper shield layer via an adhesive.
Nevertheless, since the copper foil as the fundamental shield layer described above has metallic luster, there is a problem in that it reflects light from outside the panel, contrast of the screen becomes inferior, reflects light generated inside the screen, optical transmission will deteriorate, and visibility of the display panel will deteriorate.
In light of the foregoing problems, blackening treatment is performed to a copper foil shield layer that is effective in shielding the leakage of electromagnetic waves and the line spectrum of the near infrared region.
As a conventional copper foil, known is a copper foil with a black surface coating formed thereon, and this is generally referred to as a black-treated copper foil. Nevertheless, this kind of copper foil was used in forming circuits in electronics devices, and was primarily demanded of adhesiveness with the resin or drillability with a laser beam, and was not demanded of strict surface conditions such as the smoothness or uniformity of the black-treated coating.
Nevertheless, characteristics of the copper foil that appear at the front surface of the plasma display panel directly influence the visibility of the display panel, and the development of a copper foil capable of satisfying such demands is being desired.
Although several characteristics are demanded in the black-treated coating of a plasma display panel copper foil; in particular, 1) sufficient contrast and blackness, 2) inhibition of reflected light of incoming light from the outside and reflected light of outgoing light from the plasma display panel, and 3) enablement of linear etching at a width of 5 to 30 μm, optical value of 10 μm, and pitch of 100 to 500 μm upon forming a pattern on the copper foil are demanded.
In light of the above, a shield layer formed from a copper foil is demanded of a function as a protective film of the plasma display panel, function of preventing electromagnetic waves, function of preventing near infrared rays, function of correcting the tone, function of preventing stray light, function of blocking outside light, and particularly the quality and characteristics of a blackening-treated film. Conventionally, it could be said that there was no plasma display panel copper foil that sufficiently satisfied the foregoing functions.
As conventional technology, there is technology of forming a black-edged layer at the periphery on one surface of a glass substrate as a transparent base material, forming a PET (polyethylene terephthalate) film as a transparent film on the surface thereof via a first adhesive layer, and forming a copper layer pattern as a metallic layer pattern on the PET film via an adhesive layer, wherein the copper layer pattern is formed covering the periphery of the PET film, and blackening treatment is performed to both surfaces and all side faces thereof (e.g., refer to Patent Document 1), and there is technology relating to a surface discharge plasma display panel and plasma display module in which a common electrode and scanning electrode are formed on the same surface and surface discharge is generated between the two electrodes (e.g., refer to Patent Document 2).
Further, there is technology relating to a filter device in which the transparency of the copper foil mesh filter for shielding the leaked electromagnetic waves of the optical filter provided to the front face of the PDP has been improved (e.g., refer to Patent Document 3), and there is technology of manufacturing an electromagnetic wave shield by laminating a porous copper foil on a transparent polymer film, etching the copper foil with the wet method, and, for instance, forming a lattice pattern so as to prepare a laminated body with a portion having optical transparency, and combining such laminated body, transparent support and antireflection film (e.g., refer to Patent Document 4).    [Patent Document 1] Japanese Patent Laid-Open Publication No. 2002-9484    [Patent Document 2] Japanese Patent Laid-Open Publication No. 2000-89692    [Patent Document 3] Japanese Patent Laid-Open Publication No. 2001-147312    [Patent Document 4] Japanese Patent Laid-Open Publication No. 2001-217589